The present invention relates to optics and, more particularly, to optical switches.
Much of modern progress is associated with advances in computer and related technologies that generate exponentially increasing amounts of data, often exceeding the data-handling capacity of available communications channels. Accordingly, there has been a trend toward optical communications systems, which tend to offer greater capacity or xe2x80x9cbandwidthxe2x80x9d than electrically based communications systems.
One of the challenges confronting the development of optical communications is to develop optical analogues of devices used in electrical communications systems. For an example in which an analog has been successfully developed, optical fibers serve as an analogue for electrical cables. On the other hand, matrix switching is an area where further work is required in the optical domain.
Matrix switches are used for selectively routing individual input channels to individual output channels. While it is possible to convert optical signals to electrical signals and back to allow electrical matrix switches to be used, there are costs and latencies involved in the conversions. Accordingly, optical matrix switches have been developed that avoid the need for the conversion to the electrical domain.
Optical matrix switches have been developed having grids of intersecting waveguides. Switch elements at the intersections determine whether an optical signal is transmitted straight through the intersection or reflected along an orthogonal waveguide. To this end, the intersection may alternatively be filled with index-matching (for transmission) or non-index-matching (for reflection) fluid.
For example, Agilent Technologies has introduced its xe2x80x9cChampagnexe2x80x9d photonic switch platform. In this case, a chamber at a waveguide intersection is filled with index-matching fluid. The fluid can be heated so that a non-index-matching bubble is formed. Thus, the presence of the bubble causes light to be reflected, while the absence of the bubble causes light to be transmitted. Capillary geometry and wetting properties can stabilize the bubble to establish the desired switching condition. However, such switches require a constant supply of power to maintain the vapor bubble, although power need not be continually supplied to maintain the non-bubble condition. In this sense, then, the optical switch is stable only in the non-bubble condition, and is non-stable in the bubble condition. Such bubble-based switches are therefore problematic in applications where power consumption and/or power supply reliability are a problem. In addition, bubble switches can suffer from vapor lock caused by inadequate bubble removal. Champagne photonic switches are disclosed in European Patent Application No. 1,014,140, claiming priority to U.S. patent application Ser. No. 09/221,655, filed Dec. 23, 1998, both of which references are incorporated by reference. NTT Electronics has recently offered a thermo-capillary optical switch that is xe2x80x9cself-latching.xe2x80x9d The switch relies on an oil latching interfacial variation effect, or xe2x80x9cOLIVE,xe2x80x9d where index-matching oil is injected into a micro driving slit at the point where two waveguides intersect. When the surface tension of the oil is decreased by heating, thermo-capillary forces move the oil column towards the lower-temperature side of the slit. Once the oil is away from the intersection of the waveguides, the light path is switched by total internal reflection on the slit side wall. Although the OLIVE switch provides for latched operation, the actuation mechanism is inherently slow due to the large thermal mass that must be heated in order to change the state of the switch.
Thus, it should be appreciated that fast bi-stable optical switches are needed that preferably do not suffer from vapor lock.
The present invention provides for pressure-actuated bi-stable optical switching. Thus, an inventive switch and method uses pressure to move an index-matching liquid into and out of an optical path. Pressure is generated to move the liquid within a cavity that intersects the optical path. When the pressure moves the liquid into the optical path, light is transmitted; when the liquid is moved out of the optical path, light is reflected. In the absence of pressure, the liquid position can be maintained using a number of different phenonema. In addition to providing an individual switch element and a method, the invention provides for a matrix switch with pressure-actuated bi-stable switch elements, optical systems incorporating such switches, and corresponding methods.
The pressure can be applied by heating gas within the cavity. For example, the cavity can include gas reservoirs at opposite ends of the cavity; the liquid can be moved by heating the reservoir adjacent the fluid. In some embodiments, not all the liquid is moved; instead the pressure cleaves a slug of liquid forcing only a portion to move. When the liquid motion is reversed, the portion of the liquid that did not move helps stablize the returned liquid using surface tension. In addition to or in lieu of this mechanism, various embodiments of the invention use capillary shape or wettability profile or both to achieve latching.
The present invention differs in part from the Champagne technology described in the previous section in that the xe2x80x9cmotivatingxe2x80x9d gas is not generated from the index-matching liquid, but can be separate. Accordingly, the gas need not be created and removed, but simply expands and contracts. Thus, the problem of vapor lock facing Champagne technology can be avoided by the present invention. In addition, since a bubble need not be sustained to make the intersection non-index-matching, the inventive switch is bi-stable (self-latching in both conditions). In comparison to the OLIVE technology, the invention can provide for much faster switching, as the thermal mass that must be heated to move the index-matching fluid can be much less. Other advantages, in addition to or in lieu of the foregoing, are provided by certain embodiments of the invention as is apparent from the description below with reference to the following drawings.